base 64

file format, algorithm A file format using 64 ASCII

characters to encode the six bit binary data values 0-63.

To convert data to base 64, the first byte is placed in the

most significant eight bits of a 24-bit buffer, the next in

the middle eight, and the third in the least significant eight

bits. If there a fewer than three bytes to encode, the

corresponding buffer bits will be zero. The buffer is then

used, six bits at a time, most significant first, as indices

into the string

"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"

and the indicated character output. If there were only one or

two input bytes, the output is padded with two or one "="

characters respectively. This prevents extra bits being added

to the reconstructed data. The process then repeats on the

remaining input data.

Base 64 is used when transmitting binary data through

text-only media such as electronic mail, though uuencode

is more common.

(1995-03-21)